JP5425672B2 - Manufacturing method of light diffusion film - Google Patents

Description

  The present invention relates to a method for producing a light diffusing film used in a liquid crystal display device or the like, or a polarizer protective film having a light diffusing function.

  Currently, liquid crystal display devices are used in a wide range of fields such as mobile phones, digital cameras, televisions, personal computer displays, and notebook computers. In a liquid crystal display device, various optical films such as a light diffusion film and a polarizing film are used in order to maintain the display quality. In particular, the light diffusing film is used for supplying a uniform surface light source as a point light source or a line light source of a backlight device of a liquid crystal display device. In addition, the liquid crystal display device is required not only to supply uniform light but also to supply as much light as possible in order to make the display image easy to see. Therefore, the light diffusing film is required to have an optical property of being excellent in light diffusibility and obtaining high brightness.

  As such a light diffusing film, a light diffusing film in which a light diffusing layer containing a light diffusing agent including a transparent binder resin and transparent fine particles is generally provided on one side of a support is used.

  Patent Document 1 discloses a light diffusion film having improved light diffusibility and brightness by coating a (meth) acrylic resin containing inorganic ultrafine particles and organic-inorganic composite ultrafine particles as a light diffusion layer on a transparent support. Is listed.

  However, there is a problem that the total light transmittance is low and the luminance is lowered because inorganic fine particles having a large refractive index difference from the transparent binder resin are used in order to improve the warp of the film, the deflection and the falling off of the light diffusing agent. It was. Furthermore, in the case of laminating a resin containing fine particles, there is a problem that the adhesiveness between the transparent support and the light diffusion layer is lowered due to the influence of the fine particles, so that the resin is easily peeled off.

JP 2007-272208 A

  The subject of this invention is providing the light-diffusion film which has high total light transmittance, suppressing peeling of a light-diffusion layer, a curvature, a bending, and dropping-off of a light-diffusion agent.

  As a result of intensive studies based on the above problems, the present inventors have prescribed the temperature of each step, the step of obtaining a resin solution, the step of obtaining a coating film, the step of drying the coating film, and the temperature of each step. By using a large resin, it becomes possible to apply the same resin as the transparent support, thereby suppressing light reflection at the interface between the transparent support and the light diffusion layer, peeling of the light diffusion layer, The present inventors have found that the warpage and deflection due to the dimensional change difference between the material and the light diffusion layer, and the falling off of the light diffusing agent are suppressed, leading to the present invention.

  That is, the present invention is a method for producing a light diffusing film in which a light diffusing layer containing a light diffusing agent and a second resin is present on one side or both sides of a transparent support containing the first resin. Dissolving a second resin in a solvent at a first temperature to obtain a resin solution, applying the solution to one or both surfaces of the transparent support at a second temperature to obtain a coating film, and at least applying the coating film A step of drying at a third temperature to obtain a light diffusion layer, wherein the first temperature is higher than the second temperature and lower than the third temperature; These resins are the same resin.

  As a further preferred embodiment, the step of drying the coating film is a step of drying at least at a fourth temperature and a third temperature. The fourth temperature is lower than the first temperature and higher than the second temperature.

  The present invention prevents light diffusion layer peeling, warpage and deflection due to the difference in dimensional change between the transparent base material and the light diffusion layer, and removal of the light diffusing agent, and achieves both high total light transmittance and light diffusibility. Can be obtained.

  The manufacturing method of the light-diffusion film which concerns on this invention has the following characteristics.

A method for producing a light diffusing film in which a light diffusing layer containing a light diffusing agent and a second resin is present on one side or both sides of a transparent support made of a first resin, wherein the method comprises the steps of: A first step of obtaining a resin solution by dissolving in a solvent at a first temperature (T1), a second step of obtaining a coating film by applying the solution to one or both sides of a transparent support at a second temperature (T2) The step of drying the coating film at least at a third temperature (T3) to obtain a light diffusion layer, wherein T1, T2, and T3 satisfy the following formula 1,
T2 <T1 <T3 (Formula 1)
A method for producing a light diffusion film, wherein the first resin and the second resin are the same resin.

  Embodiments of the present invention are described below, but are not intended to limit the scope of the present invention.

  Here, the light diffusing film is used in a broad sense as well as a narrowly defined film, that is, includes a film-like body, a plate-like body, a sheet-like body, a laminate, and the like.

  In addition, additives such as a plasticizer, an ultraviolet absorber, an antioxidant, an easy-adhesive, and a leveling agent can be added as long as the transparency and light diffusibility of the light diffusing film are not impaired.

<Transparent support>
The transparent support according to the present invention comprises a first resin described below.

  The transparent support here may be any of a film-like body, a plate-like body and a sheet-like body.

(First resin)
The first resin is substantially transparent, and preferably has a glass transition temperature of 90 ° C. or higher, more preferably 110 ° C. or higher. Below this range, the dimensional change due to the heat of the backlight or the like becomes large, and the support tends to be easily distorted or bent.

  The transparent support may be a polymer formed from a single type of monomer, a copolymer formed from two or more types of monomers, or a combination of two or more types of polymers.

  Specific materials include methacrylic resins such as polymethyl methacrylate, acrylic resins such as polymethyl acrylate, styrene resins such as polystyrene and MS resin, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polycarbonate resins, Examples thereof include cyclic olefin resins such as polyimide resins, glutarimide resins, lactone resins and norbornene resins, vinyl chloride resins, vinylidene chloride resins, and cellulose resins such as triacetyl cellulose and diacetyl cellulose. Among these, a methacrylic resin having an imide group or an acrylic resin having an imide group is preferable, and among them, a glutarimide resin is more preferable. A methacrylic resin having an imide group or an acrylic resin having an imide group is preferable as a support for a light diffusing film because of excellent mechanical properties such as transparency, heat resistance, dimensional change and strength. As used herein, a methacrylic resin having an imide group or an acrylic resin having an imide group is a resin in which a unit containing an imide bond is present in the repeating unit of the molecular chain of the methacrylic resin or acrylic resin, depending on the purpose. Thus, the content of units having an imide bond can be adjusted. In particular, a glutarimide resin containing a unit represented by the following general formula (1) and a unit represented by the following general formula (2) is particularly preferable because of its excellent transparency, heat resistance, and mechanical properties.

(Here, R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ³ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or 3 to 12 carbon atoms. Cycloalkyl group or an aryl group having 6 to 10 carbon atoms.)

(Here, R ⁴ and R ⁵ each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl having 3 to 12 carbon atoms. Group, or an aryl group having 6 to 10 carbon atoms).

(Transparent support production method)
The first resin is used for the transparent support.

  The method for producing the transparent support is not particularly limited, and the transparent support can be produced by a known method such as injection molding, melt extrusion molding, inflation molding, blow molding, compression molding, solution casting, or spin coating. Among them, it is preferable to use a melt extrusion method that does not use a solvent. According to the melt extrusion method, it is possible to reduce the manufacturing cost and the load on the working environment due to the solvent. Further, the transparent support may be used without stretching or a stretched film may be used. The stretching method is not particularly limited, and a known stretching method can be used. For example, transverse stretching using a tenter, longitudinal stretching using a roll, sequential biaxial stretching combining these, simultaneous biaxial stretching, and the like can be used.

<Light diffusion layer>
The light diffusing layer is composed of a light diffusing agent and a second resin described below, and is formed on one side or both sides of the transparent support.

(Second resin)
The second resin is substantially transparent and preferably has a glass transition temperature of 90 ° C. or higher, more preferably 110 ° C. or higher. Below this range, the dimensional change due to the heat of the backlight or the like increases, and the film tends to be distorted or bent.

  The second resin is preferably a material having the same characteristics as the first resin.

  Specific materials include methacrylic resins such as polymethyl methacrylate, acrylic resins such as polymethyl acrylate, styrene resins such as polystyrene and MS resin, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polycarbonate resins, Examples thereof include cyclic olefin resins such as polyimide resins, glutarimide resins, lactone resins and norbornene resins, vinyl chloride resins, vinylidene chloride resins, and cellulose resins such as triacetyl cellulose and diacetyl cellulose. Among these, a methacrylic resin having an imide group or an acrylic resin having an imide group is preferable, and among them, a glutarimide resin is more preferable. A methacrylic resin having an imide group or an acrylic resin having an imide group is preferable as a support for a light diffusing film because of excellent mechanical properties such as transparency, heat resistance, dimensional change and strength. As used herein, a methacrylic resin having an imide group or an acrylic resin having an imide group is a resin in which a unit containing an imide bond is present in the repeating unit of the molecular chain of the methacrylic resin or acrylic resin, depending on the purpose. Thus, the content of units having an imide bond can be adjusted. In particular, a glutarimide resin containing a unit represented by the following general formula (1) and a unit represented by the following general formula (2) is particularly preferable because of its excellent transparency, heat resistance, and mechanical properties.

(Here, R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ³ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or 3 to 12 carbon atoms. Cycloalkyl group or an aryl group having 6 to 10 carbon atoms.)

(Here, R ⁴ and R ⁵ each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl having 3 to 12 carbon atoms. Group or an aryl group having 6 to 10 carbon atoms.)

(Light diffusing agent)
As the light diffusing agent according to the present invention, known ones are used, and there is no particular limitation. However, in order to impart diffusibility, the refractive index is that of the transparent resin used in the transparent support and the light diffusing layer of the present invention. It is preferable that there is some difference. The refractive index difference between the transparent resin and the light diffusing agent is preferably 0.001 or more and 0.1 or less, more preferably 0.003 or more and 0.05 or less. If the refractive index difference exceeds 0.1, the total light transmittance may be reduced.

  Materials for the light diffusing agent include crosslinked polymer fine particles, silica fine particles, titania fine particles, etc. obtained by single polymerization or copolymerization of monomers having an essential component of acrylic acid ester, methacrylic acid ester, and aromatic vinyl. And metal oxide fine particles, carbonate fine particles, silicone fine particles, and the like. A single diffusing agent may be used, or a plurality of diffusing agents may be mixed and used.

  The shape of the light diffusing agent may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scale shape, and a crushed shape, and is not particularly limited.

  The average particle size of the light diffusing agent is preferably in the range of 1 to 50 μm. When the average particle diameter is 1 μm or less, the light transmitted through the light diffusion layer is transmitted without being diffused, and it may be difficult to obtain sufficient light diffusibility. On the other hand, when the thickness is 50 μm or more, the light diffusing agent is likely to fall off, so that the uniformity of light diffusion may be lost.

  The content of the light diffusing agent with respect to 100 parts by weight of the binder resin is desirably 5 parts by weight or more and less than 400 parts by weight, preferably 20 parts by weight or more and less than 250 parts by weight. When the content of the light diffusing agent is less than 5 parts by weight, a sufficient light diffusing effect cannot be obtained, and when it is 400 parts by weight or more, the light diffusing agent is aggregated and the total light transmittance may be significantly reduced. There is sex.

<Production method of light diffusion film>
The manufacturing method of a light-diffusion film is characterized by including the following processes.

A first step of dissolving a second resin in a solvent at a first temperature (T1) to obtain a resin solution, applying the solution to one or both sides of a transparent support at a second temperature (T2), and applying The second step of obtaining a film comprises the third step of drying the coating film at least at the third temperature (T3) to obtain a light diffusion layer, and T1, T2, and T3 satisfy the following formula 1.
T2 <T1 <T3 (Formula 1)

(First step)
The solvent in the first step has a high solubility of the second resin at the first temperature (T1) and a low solubility in the first resin at the second temperature (T2), which is the temperature at the time of application. Is desirable.

  In the present invention, since the second resin is desired to have the same characteristics as the first resin, a combination of a resin and a solvent is preferable so that the temperature dependency of the dissolution rate of the second resin is increased. .

  Furthermore, the solubility in T1 of said 1st resin and 2nd resin is 5 weight% or more, and the transparent support body which consists of 1st resin from the immersion method prescribed | regulated to JISK-5600-6-1 is T2. A combination of a solvent and a resin that does not cause pores in the transparent support at a rate of 10 μm / min or more when immersed in a solvent at a temperature is preferable. When pores are generated at a dissolution rate of 10 μm / min or more, there is a problem that the transparent support is dissolved by a solvent during coating.

  As a solvent satisfying the above, in consideration of the volatility of the solvent, it may be appropriately combined with the second resin. Specifically, for example, aromatic hydrocarbon solvents such as toluene and xylene, hexane, heptane, etc. Aliphatic hydrocarbon solvents, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as dioxolane and tetrahydrofuran, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, nitrogen-containing solvents such as dimethylformamide and dimethylacetamide Alcohol solvents such as isopropyl alcohol and butyl alcohol can be appropriately combined with the second resin listed above. These organic solvents may be used alone or in combination of two or more. A methacrylic resin or styrene resin having a glutarimide unit composed of a ketone solvent such as methyl ethyl ketone or methyl isobutyl ketone, an aromatic hydrocarbon such as toluene or xylene, and the general formulas (1) and (2) is particularly preferable. Is desirable.

  The kneading method of the light diffusing agent and the second resin is not particularly limited, and a known method can be used. Preferably, a method of dispersing the light diffusing agent in the organic solvent in advance when dissolving the transparent resin in the organic solvent is preferable from the viewpoint of the uniform dispersibility of the light diffusing agent.

  The first temperature (T1) as the dissolution temperature in the first step depends on the solubility of the second resin in the solvent, but is 65 to 80 ° C. in consideration of the temperature at the time of application and the boiling point of the organic solvent to be used. Preferably there is. More preferably, it is desirable that it is 65-75 degreeC.

(Second step)
A method for applying the second resin solution to the transparent support to obtain a coating film may be a conventionally known coating method, and is not particularly limited.

  Moreover, as 2nd temperature (T2) which is the temperature at the time of application | coating, although based on the solubility with respect to the solvent of 1st resin, it is preferable that it is 0 to 40 degreeC. More preferably, it is 10 to 35 degreeC.

(Third process)
The method for drying the coating film obtained in the second step is not particularly limited, and a conventionally known drying method may be used. The third temperature (T3), which is the temperature during drying, is preferably 80 ° C. to 120 ° C., although it depends on the solubility of the resin in the solvent and the volatility of the solvent. When the drying temperature is within the above range, the solvent in the light diffusion layer can be removed without causing deformation of the film due to heat.

  In the third step, it is more preferable to perform preliminary drying at the fourth temperature (T4) prior to drying at the drying temperature T3. The fourth temperature (T4) is preferably 40 ° C. to 65 ° C., although it depends on the solubility of the resin in the solvent and the volatility of the solvent. By drying in two steps as described above, it becomes possible to volatilize the solvent while suppressing dissolution of the transparent support, so that deformation and tearing of the transparent support can be prevented, so stable lamination Is possible.

(Temperature conditions)
The present invention is characterized in that T1, T2, and T3 satisfy the following formula 1.
T2 <T1 <T3 (Formula 1)

  It is preferable that the second resin has a large difference in solubility between T1 and T2. First, the second resin is dissolved at T1 which is higher than T2. As a result, the second resin quickly dissolves in the solvent, and the resin once dissolved hardly deposits even when T2 is reached, and the dissolved state is maintained. Next, this solution is applied to one side or both sides of the transparent support at a second temperature (T2) to obtain a coating film. Here, T2 which is a coating temperature is lower than T1 which is a temperature for rapidly dissolving the resin, and since the solubility of the resin is low, the first resin constituting the transparent support is in the solution. It is possible to minimize dissolution by the solvent. Therefore, the surface of the transparent support is not damaged more than necessary. Even if the surface is roughened, the first resin constituting the transparent support and the second resin contained in the light diffusion layer are the same resin as will be described later, and as a result, uniformity is maintained. The optical properties such as interface reflection and diffusion are hardly affected. In addition, although the solubility of the first resin in the solvent is low, it does not dissolve at all, so the adhesion with the second resin is good, because the affinity between the transparent support and the light diffusion layer is good, It is possible to prevent the light diffusion layer from peeling off and the light diffusing agent from falling off. Next, it is dried at least at a third temperature (T3) to obtain a light diffusion layer. This T3 needs to be higher than T1 as well as T2. In the drying step, as a more preferable embodiment, it is preferable to dry at a temperature (T4) higher than T2 and lower than T1 before drying at T3. Thereby, since the drying temperature is lower than T1, the possibility of dissolving the surface of the transparent support is reduced, and at the same time, the temperature is higher than T2, so that the solvent can be efficiently removed. Next, by drying at T3, even if most of the solvent is removed at T4 and then dried at T3, which is hotter than T4, the residual solvent is already low, so the surface of the transparent support is dissolved. This is preferable because the remaining solvent can be completely removed.

<Light diffusion film>
The light diffusing film according to the present invention is composed of a light diffusing layer containing a light diffusing agent and a second resin on one or both sides of a transparent support made of a first resin.

  The first resin and the second resin used in the light diffusion film according to the present invention are the same resin. By using the method for producing a light diffusing film described above, the same resin can be laminated without causing deformation or tearing of the transparent support. In addition, since the transparent support is slightly dissolved in the solvent in the second step and / or the third step, the transparent support and the light diffusion layer are in close contact, and the affinity between the transparent support and the light diffusion layer is good. Therefore, peeling of the light diffusing layer and dropping of the light diffusing agent can be suppressed.

  If it is the same resin, it becomes possible to largely suppress the interface reflection between the transparent support and the light diffusion layer, and it is possible to suppress the decrease in the total light transmittance. Further, it is possible to reduce the warpage and deflection of the film due to the difference in the dimensional change rate between the layers.

  The haze of the light diffusion film according to the present invention is preferably 30% to 95%, more preferably 40% to 90%.

  When the haze is within the above range, the light diffusion pattern of the backlight, the light guide plate, and the prism sheet can be erased, and a uniform surface light source can be obtained.

  The total light transmittance of the film according to the present invention is preferably 75% or more, more preferably 85% or more, and further preferably 90% or more.

  If the total light transmittance is within the above range, the light diffusion pattern can be erased without greatly reducing the front luminance.

  The total light transmittance and haze here are the values of the total light transmittance and haze in JIS K 7136 and JIS K7361-1, and Td (%) / Tt (%) × 100 = H (%). [Td: diffused light transmittance, Tt: total light transmittance, H: haze], measured using an optical measuring instrument called a haze meter from the uneven surface side. It is the value.

  The first resin and the second resin used in the light diffusing film according to the present invention are basically the same resin, but the same in the strict sense as long as the effects of the present invention are achieved. Not only resins but also equivalents can be included.

<Polarizer protective film>
The optical film of the present invention can be used as a polarizer protective film by being bonded to a polarizer. The polarizer is not particularly limited, and any conventionally known polarizer can be used. Specific examples include a polarizer obtained by containing iodine in stretched polyvinyl alcohol.

  When used as a polarizer protective film, it is preferable that the optical anisotropy is small.

The specific value of the orientation birefringence is preferably from 0 to 0.1 × 10 ^-3, is preferably 0 to 0.01 × 10 ^-3.

  If the orientation birefringence is within the above range, stable optical characteristics can be obtained without causing birefringence during molding even when the environment changes.

  In the present specification, unless otherwise specified, “orientation birefringence” means birefringence that develops when stretched 100% at a temperature 5 ° C. higher than the glass transition temperature of a thermoplastic resin. The orientation birefringence (Δn) is defined by Δn = nx−ny = Re / d when described using nx and ny described above, and can be measured by a phase difference meter.

In the optical film according to the present invention, the absolute value of the photoelastic coefficient is preferably 20 × 10 ⁻¹² m 2 / N or less, more preferably 10 × 10 ⁻¹² m 2 / N or less, and 5 × More preferably, it is 10 ⁻¹² m 2 / N or less.

  If the photoelastic coefficient is within the above range, even if the optical film according to the present invention is used in a liquid crystal display device, phase difference unevenness occurs, contrast at the periphery of the display screen decreases, or light leakage occurs. There is nothing to do.

On the other hand, when the absolute value of the photoelastic coefficient is larger than 20 × 10 ⁻¹² m 2 / N, when the optical film according to the present invention is used for a liquid crystal display device, unevenness in phase difference occurs, There is a tendency that the contrast is lowered and light leakage is likely to occur. This tendency becomes particularly remarkable in a high temperature and high humidity environment.

When an external force is applied to an isotropic solid to generate a stress (ΔF), it temporarily exhibits optical anisotropy and exhibits birefringence (Δn). In this specification, the photoelastic coefficient means the ratio of the stress to birefringence. That is, the photoelastic coefficient (c) is calculated by the following equation.
c = Δn / ΔF
However, in the present invention, the photoelastic coefficient is a value measured at 23 ° C. and 50% RH at a wavelength of 515 nm by the Senarmon method.

(For light diffusion film)
Although the use of the light diffusion film according to the present invention is not particularly limited, specifically, for example, imaging fields such as cameras, VTRs, projectors, viewfinders, filters, prisms, and Fresnel lenses, CD players Information equipment field such as lens field such as optical disk pickup lens such as DVD player, MD player, optical recording field, liquid crystal light guide plate, liquid crystal display film such as polarizer protective film and retardation film, surface protective film, etc. Optical communication field such as optical fiber, optical switch, optical connector, automotive field such as automobile headlight and tail lamp lens, inner lens, instrument cover, sunroof, eyeglasses, contact lens, endoscope lens, medical treatment requiring sterilization Medical equipment field such as supplies, road transparency Plates, glazing lenses, lighting window and a carport, an illumination lens and light cover, architectural and alive areas such as building materials for sizing, can be suitably used for microwave cooking vessel (dishes) or the like.

  As described above, the optical film according to the present invention is excellent in optical characteristics such as optical homogeneity and transparency. Therefore, by utilizing these optical characteristics, it can be particularly suitably used for known optical applications such as the periphery of liquid crystal display devices such as an optical isotropic film, a polarizer protective film, an antireflection film, and a transparent conductive film.

  Here, although one Embodiment of the method to manufacture the film concerning this invention is described, this invention is not limited to this.

<Evaluation method>
(Haze)
The haze was measured by irradiating light from the light diffusion layer side using a haze meter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. based on the method described in JIS K7136.

  (Total light transmittance) Total light transmittance was measured by irradiating light from the light diffusion layer side using a haze meter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. based on the method described in JIS K 7361-1. .

(Adhesion)
Adhesion between the transparent support and the light diffusing layer is evaluated by applying an adhesive tape to the surface of the light diffusing layer of the produced light diffusing film and peeling it off strongly. The degree of peeling of the light diffusing layer is determined according to the following three criteria. Was evaluated.
○: No peeling.
Δ: Partial peeling or light diffusing agent falling off.
X: There is much peeling.

(warp)
The evaluation of warpage and deflection of the light diffusion film was performed visually, and the evaluation was performed according to the following criteria.
○: No warping or deflection is seen.
X: Warp and deflection can be confirmed.

(Preparation of glutarimide resin)
A glutarimide resin was produced using commercially available polymethyl methacrylate (Kuraray Co., Ltd.) and monomethylamine (Mitsubishi Gas Chemical Co., Ltd.) as an imidizing agent. The extruder used was a meshing type co-rotating twin screw extruder having a diameter of 15 mm. The set temperature of each temperature control zone of the extruder is 200 to 280 ° C., the screw rotation speed is 55 rpm, polymethyl methacrylate is supplied at 150 kg / hr, and the supply amount of monomethylamine is 2 parts by weight with respect to polymethyl methacrylate. did. Polymethyl methacrylate was charged from the hopper, and the resin was melted and filled with the kneading block, and then monomethylamine was injected from the nozzle. A seal ring was placed at the end of the reaction zone to fill the resin. By-products and excess methylamine after the reaction were removed by reducing the pressure at the vent port to -0.099 MPa. The resin that came out as a strand from a die provided at the exit of the extruder was cooled in a water tank and then pelletized with a pelletizer.

  Next, in a mesh type co-rotating twin screw extruder with a diameter of 15 mm, the set temperature of each temperature control zone of the extruder is 200 to 260 ° C., the screw rotation speed is 55 rpm, and polymethyl methacrylate is supplied at 150 kg / hr. After melting and filling the resin with a kneading block, a mixture of 0.8 parts by weight of dimethyl carbonate and 0.2 parts by weight of triethylamine is injected from the nozzle into the resin to reduce the carboxyl groups in the resin. Went. A seal ring was placed at the end of the reaction zone to fill the resin. By-products after reaction and excess dimethyl carbonate were removed by reducing the pressure at the vent port to -0.099 MPa. The resin that came out as a strand from a die provided at the exit of the extruder was cooled in a water tank and then pelletized with a pelletizer.

Further, in a mesh type co-rotating twin screw extruder having a diameter of 15 mm, the set temperature of each temperature control zone of the extruder was 260 ° C., the screw rotation speed was 55 rpm, and polymethyl methacrylate was supplied at 150 kg / hr. The pressure at the vent port was reduced to -0.099 MPa to remove volatile components such as unreacted auxiliary materials again. The resin coming out as a strand from the die provided at the exit of the extruder is cooled in a water tank and then pelletized with a pelletizer, whereby R ¹ and R ³ in the above general formulas (1) and (2), A glutarimide resin in which R ⁵ and R ⁶ are each a methyl group and R ² and R ⁴ are each a hydrogen atom was obtained.

Imidization ratio is used SensIR Technologies Inc. TravelIR measuring device, and the absorption derived from ester carbonyl groups near 1720 cm ^-1, was determined from the intensity ratio of the absorption derived from the imide carbonyl groups near 1660 cm ^-1. Here, the imidation rate refers to the proportion of the imide carbonyl group in all the carbonyl groups.

  The glass transition temperature was measured using a differential scanning calorimeter (DSC, Shimadzu Corporation DSC-50) under a nitrogen atmosphere at a heating rate of 20 ° C./min and determined by the midpoint method.

  The photoelastic coefficient was measured at a wavelength of 515 nm at a temperature of 23 ± 2 ° C. and a humidity of 50 ± 5% using a micro-polarization spectrophotometer (TFM-120AFT-PC manufactured by Oak Seisakusho). In the measurement, the birefringence was measured with one film fixed and the other loaded with no load and a load of 500 g, and the amount of change in birefringence due to unit stress was calculated from the obtained results.

For the glutarimide resin used in this example, the imidization rate, glass transition temperature, and photoelastic coefficient were measured according to the above-described methods. As a result, the imidation ratio was 13 mol%, the glass transition temperature was 127 ° C., and the photoelastic coefficient was −3 × 10 ⁻¹² m ² / N.

(Light diffusing agent)
A light diffusing film was produced using the following as the light diffusing agent in Examples and Comparative Examples.
Diffusing agent A
GM-0401S manufactured by Ganz Kasei Co., Ltd.
Particle size 4μm Crosslinked polymethyl methacrylate fine particle refractive index 1.49
Diffusing agent B
GM1001S manufactured by Ganz Kasei Co., Ltd.
Particle size 10 μm Crosslinked polymethyl methacrylate fine particle refractive index 1.49
Diffusing agent C
GM-2003S-S manufactured by Ganz Kasei Co., Ltd.
Particle size 20 μm Crosslinked polymethyl methacrylate fine particle refractive index 1.49
Diffusion agent D
SI-030 manufactured by Ganz Kasei Co., Ltd.
Particle size 3 μm silica particle refractive index 1.41.

Example 1
In preparing the coating solution for the light diffusing layer, 100 parts by weight of the glutarimide resin prepared by the method described above as a binder resin and 25 parts by weight of the light diffusing agent A are added to 300 parts by weight of methyl isobutyl ketone as a solvent. Stirring was performed until the resin was completely dissolved at a temperature of 70 ° C. and the solution was uniform. Thereafter, the coating liquid was cooled to 20 ° C. to obtain a light diffusion layer coating liquid.
The light diffusion layer coating solution prepared on one side of a glutarimide resin film (40 μm) was applied at 20 ° C., dried in an oven at 60 ° C. to remove most of the solvent, and then left at 80 ° C. By removing the solvent, a light diffusion film having a light diffusion layer thickness of 5 μm was obtained.

(Example 2)
A light diffusion film was produced using the same method as in Example 1 except that the light diffusion layer was applied to have a thickness of 20 μm.

(Example 3)
A light diffusing film was produced in the same manner as in Example 1 except that the number of parts of the light diffusing agent A was 100 parts by weight.

Example 4
A light diffusing film was produced using the same method as in Example 2 except that the number of parts of the light diffusing agent A was 100 parts by weight.

(Example 5)
A light diffusion film was produced in the same manner as in Example 1 except that the number of parts of the light diffusing agent A was 233 parts by weight.

(Example 6)
A light diffusing film was produced in the same manner as in Example 2 except that the number of parts of the light diffusing agent A was 233 parts by weight.

(Example 7)
A light diffusing film was produced using the same production method as in Example 1 except that the number of parts of the light diffusing agent A was 400 parts by weight and that the thickness of the light diffusing layer was 10 μm.

(Example 8)
Instead of using 25 parts by weight of light diffusing agent A, 100 parts by weight of light diffusing agent B was used, and the same production method as in Example 1 was used, except that the thickness of the light diffusing layer was 21 μm. Thus, a light diffusion film was produced.

Example 9
Instead of using 25 parts by weight of light diffusing agent A, 100 parts by weight of light diffusing agent C was used, and the same production method as in Example 1 was used, except that the thickness of the light diffusing layer was 25 μm. Thus, a light diffusion film was produced.

(Example 10)
Instead of using 25 parts by weight of the light diffusing agent A, 100 parts by weight of the light diffusing agent D was used, and the same production method as in Example 1 was used except that the thickness of the light diffusing layer was 10 μm. Thus, a light diffusion film was produced.

(Comparative Example 1)
A light diffusing film was produced in the same manner as in Example 2 except that no light diffusing agent was added.

(Comparative Example 2)
In Example, a light diffusion film was produced in the same manner as in Example 3 except that polyethylene terephthalate (Lumirror R41 manufactured by Toray Industries, Inc.) was used as the transparent support.

(Comparative Example 3)
In Examples, a light diffusion film was produced in the same manner as in Example 4 except that cellulose acetate propionate resin (CAP482-0.5 manufactured by Eastman Chemical) was used as the binder resin of the light diffusion layer.

  Table 1 shows the blending amount of each component of the coating liquid for light diffusion layer and the characteristics of the obtained film in each Example and Comparative Example.

  In this way, the resin used for the transparent support and the binder resin are the same resin, and by laminating the light diffusing layer from the above three steps, a light diffusing film with high deformation and peeling and high total light transmittance can be obtained. It is done.

Claims (7)

A method for producing a light diffusing film in which a light diffusing layer containing a light diffusing agent and a second resin is present on one side or both sides of a transparent support made of a first resin,
The manufacturing method includes:
A first step of dissolving a second resin in a solvent at a first temperature (T1) to obtain a resin solution;
A second step of applying the solution to one or both surfaces of the transparent support at a second temperature (T2) to obtain a coating film;
A third step of drying the coating film at least at a third temperature (T3) to obtain a light diffusion layer;
T1, T2, and T3 satisfy the following formula 1,
T2 <T1 <T3 (Formula 1)
The manufacturing method of the light-diffusion film characterized by the 1st resin and 2nd resin being the same resin. The third step includes a step of drying at a fourth temperature (T4) before drying at the third temperature,
The light diffusion film manufacturing method according to claim 1, wherein the following formula 2 is satisfied.
T2 <T4 <T1 (Formula 2)   The solubility of the first resin and the second resin at T1 is 5% by weight or more, and the transparent support made of the first resin is subjected to the temperature of T2 by the dipping method defined in JIS K-5600-6-1. The method for producing a light diffusing film according to claim 1, wherein a solvent that does not cause pores in the transparent support is used at a rate of 10 μm / min or more when immersed in a solvent.   The said 1st resin and 2nd resin are methacrylic resin which has an imide group, or acrylic resin which has an imide group, The manufacture of the light-diffusion film of any one of Claims 1-3 characterized by the above-mentioned. Method.   5. The method for producing a light diffusing film according to claim 4, wherein the methacrylic resin having an imide group or the acrylic resin having an imide group is a glutarimide resin. The method for producing a light diffusion film according to claim 5, wherein the glutarimide resin includes a unit represented by the following general formula (1) and a unit represented by the following general formula (2).

(Here, R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ³ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or 3 to 12 carbon atoms. Cycloalkyl group or an aryl group having 6 to 10 carbon atoms.)

(Here, R ⁴ and R ⁵ each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl having 3 to 12 carbon atoms. Group or an aryl group having 6 to 10 carbon atoms.)   The manufacturing method of the polarizer protective film characterized by using the light-diffusion film of any one of Claims 1-6.